While techniques of open domain dialogue generation [1]}, [2]}, [3]} have been applied in industrial products [4]}, [5]}, people can still feel the gap between the dialogue systems and humans, especially when they dive into a specific topic of interest. To bridge the gap, researchers consider grounding open domain dialogues by external knowledge which could be retrieved either from structured knowledge bases [6]}, [7]}, [8]} or from unstructured documents [9]}.
Dialogue generation now is based on both conversation contexts and the external knowledge which hints the generation model how to go deep for the topic in discussion.
